In aged humans, low-intensity exercise increases mitochondrial density, function and oxidative capacity, decreases the prevalence of hybrid fibers, and increases lean muscle mass, but these adaptations have not been studied in aged horses. Effects of age and exercise training on muscle fiber type and size, satellite cell abundance, and mitochondrial volume density (citrate synthase activity; CS), function (cytochrome c oxidase activity; CCO), and integrative (per mg tissue) and intrinsic (per unit CS) oxidative capacities were evaluated in skeletal muscle from aged (n = 9; 22 ± 5 yr) and yearling (n = 8; 9.7 ± 0.7 mo) horses. Muscle was collected from the gluteus medius (GM) and triceps brachii at wk 0, 8, and 12 of exercise training. Data were analyzed using linear models with age, training, muscle, and all interactions as fixed effects. At wk 0, aged horses exhibited a lower percentage of type IIx (p = 0.0006) and greater percentage of hybrid IIa/x fibers (p = 0.002) in the GM, less satellite cells per type II fiber (p = 0.03), lesser integrative and intrinsic (p≤ 0.04) CCO activities, lesser integrative oxidative phosphorylation capacity with complex I (PCI; p = 0.02) and maximal electron transfer system capacity (ECI+II; p = 0.06), and greater intrinsic PCI, ECI+II, and electron transfer system capacity with complex II (ECII; p≤ 0.05) than young horses. The percentage of type IIx fibers increased (p < 0.0001) and of type IIa/x fibers decreased (p = 0.001) in the GM, and the number of satellite cells per type II fiber increased (p = 0.0006) in aged horses following exercise training. Conversely, the percentage of type IIa/x fibers increased (p ≤ 0.01) and of type IIx fibers decreased (p ≤ 0.002) in young horses. Integrative maximal oxidative capacity (p ≤ 0.02), ECI+II (p ≤ 0.07), and ECII (p = 0.0003) increased for both age groups from wk 0 to 12. Following exercise training, aged horses had a greater percentage of IIx (p ≤ 0.002) and lesser percentage of IIa/x fibers (p ≤ 0.07), and more satellite cells per type II fiber (p = 0.08) than young horses, but sustained lesser integrative and intrinsic CCO activities (p≤ 0.04) and greater intrinsic PCI, ECI+II, and ECII (p≤ 0.05). Exercise improved mitochondrial measures in young and aged horses; however, aged horses showed impaired mitochondrial function and differences in adaptation to exercise training.

To test the hypothesis that complexed trace mineral supplementation would increase antioxidant capacity and decrease muscle oxidative stress and damage in young horses entering an exercise training program, Quarter Horses (mean $$\pm$$ ± SD; 9.7 ± 0.7 mo) balanced by age, sex, and BW were assigned to receive complexed (CTM; n = 8) or inorganic (INORG; n = 8) trace minerals at -12 week relative to this study. Blood and muscle samples were collected before (week 0) and after 12 week of light exercise training surrounding a 1.5-h trailer stressor. Muscle glutathione peroxidase (GPx) activity was higher for CTM than INORG horses (P ≤ 0.0003) throughout the study. Following both trailer stressors, serum creatine kinase increased (P < 0.0001) and remained elevated through 24 h post-trailering (P < 0.0001). At week 0, muscle malondialdehyde, expression of superoxide dismutase 2, and whole blood GPx activity increased (P$$\le$$ ≤ 0.003) following trailering but trailering did not affect these measures at week 12. Young horses supplemented with CTM had higher muscle GPx activity than horses receiving INORG, but CTM did not affect damage markers following a stressor. Dietary CTM may be useful for improving antioxidant capacity during exercise training in young equine athletes.

Conjugated linoleic acid (CLA) improves oxidative stress and mitochondrial biogenesis in various species but has not been thoroughly investigated in horses. We collected blood and muscle samples from lightly exercising horses before and 6 and 12 wk after receiving either soybean oil (CON; n = 5) or CLA (CLA; n = 5) supplementation. Samples were analyzed for markers of mitochondrial characteristics, antioxidant status, oxidative stress, and muscle damage. Data were analyzed using a linear model with repeated measures. In the triceps brachii (TB), citrate synthase (CS) activity was higher in CON than CLA horses (P = 0.003) but was unaffected by diet in the gluteus medius (GM). Integrative (relative to mg protein) cytochrome c oxidase (CCO) activity was higher in TB than the GM (P &lt; 0.0001), while intrinsic (relative to CS) CCO was lower in the TB than the GM (P = 0.02) and tended to be lower in CON than CLA horses (P = 0.06). Neither CS nor integrative CCO activities were affected by time. In the GM, superoxide dismutase activity tended to increase in CON through wk 12 (P = 0.10). Over both muscle groups, glutathione peroxidase activity tended to be higher in CON compared to CLA at wk 12 (P = 0.06). Malondialdehyde was higher in the TB than the GM (P = 0.0004) but was unaffected by diet, while serum creatine kinase activity tended to be lower in CLA than CON horses (P = 0.07). These results suggest that CLA supplementation may lead to mitochondrial adaptations and prevent myofiber perturbation in skeletal muscle of young, lighlty exercised horses.

Sixteen Quarter Horse mares (mean±SEM; 12±5 yr; 5.1±1.0 BCS; 579±9 kg BW) were used to evaluate the time course of the nutrient profile of colostrum and milk following parturition. Mares received a commercial concentrate designed to meet NRC (2007) requirements for gestating mares and were fed to maintain a BCS between 5 and 7. Horses were group housed in dry lots with ad libitium access to coastal Bermudagrass hay and water. As soon as parturition was observed, colostrum was collected by hand pre-suckle (0 h post-parturition), and at 6, 12, 24, and 36 h post-parturition. Samples were evaluated for concentrations of protein, fat, lactose, somatic cell count (SCC), urea nitrogen, and non-fat solids (NFS) by a commercial laboratory. Differences between means were determined using PROC MIXED in SAS (v9.4) with time as a repeated measure. Following parturition, colostrum protein and NFS decreased from h 0 to 6 (protein: 13.1±0.7 to 9.7±0.8%; NFS: 20.9±0.8 to 16.8±0.9%) and from h 6 to 12 (P0.04). Protein continued to show a trend for a decrease from h 12 to 24 (P = 0.08), plateauing around 3%. NFS remained around 10% from h 12 to 36. Conversely, lactose did not change from h 0 to 6 (3.6±0.2 to 3.9±0.2%) but increased from 6 to 12 h (5.5±0.2%) post-parturition (P &lt; 0.0001). Fat, SCC, and urea nitrogen remained unchanged through 36 h post-parturition. These results indicate colostrum protein concentration decreases as early as 6 h post-parturition, and the non-fat solid portion of milk shifts from primarily proteins to lactose. However, the impact of these changes on foal health should be more clearly defined.